1. Field of the Invention
This invention relates to optically readable digital data storage media, and more particularly, to optically readable thin film digital data storage media adapted to be compatible with CD audio and CD ROM playing equipment.
2. Description of the Prior Art
Compact discs or CD's have the capability of storing approximately 600 megabytes of digitized audio signals (CD audio) or digital data in a computer readable format (CD ROM).
Conventional CD discs are fabricated as standard-size rigid plastic discs by means of a mold-based replication system using injection molding techniques. Such CD manufacturing techniques have the capability of producing CD discs at the rate of only approximately twenty units per minute per mold. As a result of this relatively slow production rate, the cost of producing CD's is relatively high. The essentially all-plastic composition of CD's requires the consumption of a relatively significant amount of plastic during the manufacturing process.
Each CD includes a series of either circular or spiral data tracks which are illuminated and read by a source of coherent light such as a laser. The layer of rigid plastic positioned between each data track and the source of coherent light provides structural rigidity, protects the data tracks, and also functions as a single element, integral lens element having a forty-seven millimeter optical path length to refract and focus the coherent light beam onto a selected data track.
The relatively high cost of the CD plastic content and the slow injection molding production techniques involved in mass producing CD's has maintained the cost of this digital data storage medium relatively high.